(1) Field of the Invention
The present invention relates to a printed circuit board having a positioning hole.
(2) Description of Related Art
A printed circuit board having a positioning hole is disclosed in Unexamined Japanese Patent Publication No. 2004-341102. More specifically, FIGS. 5A and 5B show schematic sectional views of a printed circuit board 50 to mount an optical semiconductor element S thereon as a conventional printed circuit board having a positioning hole. The conventional printed circuit board 50 to mount the optical semiconductor element S thereon has a plurality of semiconductor element connection pads 12 to which electrodes T of the optical semiconductor element S are connected on an upper surface of an insulating substrate 11. The semiconductor element connection pads 12 have outer peripheries covered with a solder resist layer 13 coated on the upper surface of the insulating substrate 11, and have central portions exposed in an opening 14 formed in the solder resist layer 13. The electrodes T of the optical semiconductor element S and the exposed portions of the semiconductor element connection pads 12 are electrically connected to each other by flip chip bonding through solder bumps B. A penetrating window 15 to make it possible to exchange light with the optical semiconductor element S is formed at a central portion of the insulating substrate 11. The penetrating window 15 is formed to face a light-receiving or light-emitting unit L of the optical semiconductor element S. A guide hole 16 to position an optical fiber F is formed in an outer periphery of the insulating substrate 11.
On the other hand, the optical fiber F is connected to a lower-surface side of the insulating substrate 11. The optical fiber F is supported by a guide member G. A guide pin P for positioning at a position corresponding to the guide hole 16 is arranged in the guide member G. The guide pin P is inserted into the guide hole 16 to position the optical fiber F with respect to the light-receiving or light-emitting unit L of the optical semiconductor element S.
The guide hole 16 is generally formed with drilling. A positioning accuracy of the guide hole 16 by drilling is about ±50 μm. The exposed portions of the semiconductor element connection pads 12 to which the electrodes T of the optical semiconductor element S are connected are defined by the opening 14 of the solder resist layer 13 coated on the insulating substrate 11. The solder resist layer 13 is normally formed such that a paste-formed or film-like resin composition for solder resist layer 13 having photosensitivity is applied or attached to the insulating substrate 11 on which the semiconductor element connection pads 12 are formed, exposed and developed by using a known photolithography technique into a pattern having the opening 14, and thermo-set. At this time, a positioning accuracy of the opening 14 is about ±15 μm. Therefore, a positioning accuracy between the optical semiconductor element S and the guide hole 16 exceeds ±60 μm because the optical semiconductor element S and the guide hole 16 overlap. For this reason, in the conventional printed circuit board 50, since the positioning accuracy between the optical semiconductor element S and the guide hole 16 is low, the light-receiving or light-emitting unit L of the optical semiconductor element S and the optical fiber F are difficult to be accurately positioned.